1. Field of the Invention
The invention relates generally to internal fracture fixation devices and, in particular, to intramedullary nail systems for the internal fracture fixation of long bones.
2. Description of the Prior Art
Intramedullary nails have long been used for internal fracture fixation. Generally, such a device comprises an extended hollow shaft having a predetermined cross-section and provided with transverse apertures at selected locations along its length. The nail is inserted into an intramedullary canal of a long bone and secured within the bone by transverse bone screws placed through aligned apertures in the nail.
Because the length of the intramedullary nail must be matched to the length of the bone to be repaired, prior art intramedullary nails are produced in a variety of lengths and diameters. In order to limit the number of sizes which must be carried in inventory, recent intramedullary nails have been produced as modular systems having a limited number of base nail members provided in a uniform length and a much larger variety of extension members in varying lengths and diameters. A selected extension member can be joined to any selected base nail member to produce an intramedullary nail of any desired length.
An additional consideration with intramedullary nails is that they must be transversely secured within the bone as mentioned above. Some bone screws are usually inserted in the proximal and distal ends of the nail, the former being often tilted to engage the femoral head with a certain degree of anteversion. Because the intramedullary nails generally have a cross-section which prevents their rotation within the intramedullary canal, the nail must be inserted into the canal with the proximal transverse openings generally aligned with the proper degree of anteversion in order to enable the transverse bone screws to be received within the femoral head. With respect to unitary intramedullary nails (as opposed to the aforementioned modular intramedullary nails), such as, for example, the unitary intramedullary nail shown in U.S. Pat. No. 4,622,959 (Marcus), once the nail is inserted into the canal, it cannot be rotated and, therefore, rotational positioning is somewhat critical prior to insertion of the nail into the canal. While modular intramedullary nail systems do not have quite the same limitation in anteversion adjustment of the proximal bone screw, as noted below known modular systems are limited in the available degree of anteversion adjustment.
One type of modular intramedullary nail system has been disclosed in U.S. Pat. No. 4,805,607 (Engelhardt et al.). The intramedullary nail of Engelhardt is provided with an extension member available in different lengths and diameters. While the Engelhardt device is advantageous in providing a femoral intramedullary system capable of being adapted to a variety of different length bones, it is incapable of infinite anteversion adjustment of the extension member relative to the base nail. The Engelhardt intramedullary nail secures the extension member to the end of the base nail by means of a pair of resilient tongs on the base member passing through a narrowed aperture on the extension member so that, upon engagement of the two members, axial separation is prevented although the extension member may still rotate relative to the base member. This rotation is necessary because, while the base member of the Engelhardt device does not require precise rotational positioning within the femur, the device does require a transverse screw to be threadably engaged through the extension member and between the tongs on the base member to secure the angular orientation of the extension member base member relative to the base member and to prevent the tongs from accidentally coming together and enabling axial separation of the extension from the base member. However, the Engelhardt arrangement enables the extension member to be secured in only one of two orientations relative to the tongs because the transverse locking screw must pass between the tongs. Consequently, the Engelhardt device is incapable of being easily implanted with the numerous degrees of anteversion which may be encountered by an orthopedic surgeon in various patients
It is an object of this invention to provide a modular intramedullary nail system having a plurality of base nail members suitable for use with a plurality of extension nail members of varying length and/or diameter.
It is an additional object of this invention to provide a modular intramedullary nail capable of rotatably receiving a variety of extension members of selected length, the extension members capable of being secured in any desired angular orientation relative to the base portion of the intramedullary nail while also adapted to be axially secured to prevent axial separation of the two components.